Visual estimation of coronary calcium on computed tomography for attenuation correction.

BACKGROUND: The coronary calcium score (CCS) provides independent diagnostic and prognostic information on top of myocardial perfusion imaging (MPI) in patients suspected for coronary artery disease, but requires an additional computed tomography (CT) scan. OBJECTIVE: We investigated the accuracy and inter-reader reproducibility of visual estimation of the CCS on the CT used for attenuation correction. METHODS: 250 patients undergoing single photon emission computed tomography MPI and Agatston CCS were included. The CCS was also visually estimated on the CT for attenuation correction by two separate readers blinded to the Agatston CCS, and was categorized into a six-point scale (0, 1-10, 11-100, 101-400, 401-1000 and > 1000). RESULTS: The median Agatston CCS was 82 [25th-75th percentile: 0-562], with a range from 0 to 7287. Of the visually estimated CCS, 60% (reader 1) and 65% (reader 2) were classified correctly into the 6 categories. 93% (reader 1) and 88% (reader 2) of the visually estimated CCS did not vary by more than one category from the Agatston CCS. The intraclass correlation coefficient for agreement between the Agatston CCS and the visually estimated CCS was 0.95 for reader 1 and 0.94 for reader 2. The intraclass correlation coefficient for inter-reader reproducibility of the visually estimated CCS was 0.96. CONCLUSION: The CCS can be accurately estimated on the CT for attenuation correction, as high agreement is demonstrated with the Agatston CCS and inter-reader reproducibility is excellent. If no traditional Agatston CCS is performed, the degree of atherosclerosis should be assessed by means of estimating CCS on the CT for attenuation correction.

Development and validation of a patient-tailored dose regime in myocardial perfusion imaging using conventional SPECT.

BACKGROUND: The decreasing image quality in heavier patients can be compensated by administration of a patient-specific dose in myocardial perfusion imaging (MPI) using a cadmium zinc telluride-based SPECT camera. Our aim was to determine if the same can be achieved when using a conventional SPECT camera. METHODS: 148 patients underwent SPECT stress MPI using a fixed Tc-99m tetrofosmin tracer dose. Measured photon counts were normalized to administered tracer dose and scan time and were correlated with body weight, body mass index, and mass per length to find the best predicting parameter. From these data, a protocol to provide constant image quality was derived, and subsequently validated in 125 new patients. RESULTS: Body weight was found to be the best predicting parameter for image quality and was used to derive a new dose formula; A admin (MBq) = 223·body weight (kg)(0.65)/T scan (min). The measured photon counts decreased in heavier patients when using a fixed dose (P < .01) but this was no longer observed after applying a body-weight-dependent protocol (P = .20). CONCLUSIONS: Application of a patient-specific protocol resulted in an image quality less depending on patient's weight. The results are most likely independent of the type of SPECT camera used, and, hence, adoption of patient-specific dose and scan time protocols is recommended.

Development and validation of a patient-tailored dose regime in myocardial perfusion imaging using CZT-SPECT.

BACKGROUND: Guidelines for SPECT myocardial perfusion imaging (MPI) traditionally recommend a fixed tracer dose. Yet, clinical practice shows degraded image quality in heavier patients. The aim was to optimize and validate the tracer dose and scan time to obtain a constant image quality less dependent on patients' physical characteristics. METHODS: 125 patients underwent Cadmium Zinc Telluride (CZT)-SPECT stress MPI using a fixed Tc-99m-tetrofosmin tracer dose. Image quality was scored by three physicians on a 4-point grading scale and related to the number of photon counts normalized to tracer dose and scan time. Counts were correlated with various patient-specific parameters dealing with patient size and weight to find the best predicting parameter. From these data, a formula to provide constant image quality was derived, and subsequently tested in 92 new patients. RESULTS: Degradation in image quality and photon counts was observed for heavier patients for all patients' specific parameters (P < .01). We found body weight to be the best-predicting parameter for image quality and derived a new dose formula. After applying this new body weight-depended tracer dose and scan time in a new group, image quality was found to be constant (P > .19) in all patients. CONCLUSIONS: Also in CZT SPECT image quality decreases with weight. The use of a tracer dose and scan time that depends linearly on patient's body weight corrected for the varying image quality in CZT-SPECT MPI. This leads to better radiation exposure justification.

[Regadenoson as a new stress agent in myocardial perfusion imaging. Initial experience in The Netherlands]. / El regadenosón como nuevo agente de estrés para la adquisición de imágenes SPECT de perfusión miocárdica. Experiencia inicial en Holanda.

OBJECTIVE: Regadenoson is a recently approved selective adenosine-2A receptor agonist to induce pharmacological stress in myocardial perfusion imaging (MPI) procedures using a single bolus injection. MATERIAL AND METHODS: We included 123 patients referred for MPI because of suspected coronary arterial disease (CAD). Of these, 66 patients underwent a regadenoson stress test and 57 patients underwent an adenosine stress test preceding standard myocardial SPECT imaging. Technicians, physicians and patients were asked to report their experience using questionnaires. RESULTS: As compared to adenosine, regadenoson did not produce any atrio-ventricular block (0 vs. 10% with adenosine), but did produce minor tachycardia and minimal blood pressure changes while all other side effects were milder and shorter. There were fewer patients with severe complaints after taking regadenoson than adenosine (17% vs. 32%, respectively, p<0.01). The most frequent complaint reported was dyspnea, followed by flushing and chest pain. However, when they did occur, they usually disappeared rapidly. The overall symptom score, including severity and duration of side effects, was significantly lower after regadenoson than after adenosine (6.7±6.3 vs. 10.0±7.9, respectively; p<0.01.) SPECT imaging results were similar. The regadenoson procedure was faster and more practical. CONCLUSION: Regadenoson, the new selective adenosine-2A receptor agonist, is a stress agent for MPI with a patient- and department friendly profile.

Subdural hygroma: a rare complication of spinal anesthesia.

IMPLICATIONS: We describe a patient with frontal hygroma after spinal anesthesia--a rare complication. This condition should be considered in patients after spinal anesthesia with persisting orthostatic headache. Risk factors include ventriculo-peritoneal shunt or brain atrophy caused by old age.

Changes in perfusion scintigraphy in the first days of heparin therapy in patients with acute pulmonary embolism.

Patients with suspected pulmonary embolism often receive heparin therapy for hours to days before ventilation/perfusion scintigraphy is completed. We assessed to what extent the lung scan classification and pulmonary vascular perfusion changed over a period of 2-4 days of full anticoagulant therapy. In 312 consecutive patients with at least one segmental perfusion defect on the initial perfusion scan, classification of both the initial and the final lung scan allowed us to study alteration in scan classification. Changes in pulmonary perfusion were assessed scintigraphically in a subgroup of 64 patients with proven pulmonary embolism. Among 79 patients with an initial high-probability lung scan, the final scan remained high probability in 77 whereas it became non-diagnostic and normal in one patient each. The lung scan classification did not change in any of the 233 patients who initially had a non-diagnostic scan. Thus, a different lung scan category was observed in only 2 out of 312 patients (0.6%; 95% CI 0.1%-2.3%). The mean pulmonary perfusion at baseline in the subgroup of 64 patients with pulmonary embolism was 62% (SD +/-17%; range 26%-89%). A mean absolute improvement in pulmonary perfusion of only 4%+/-11% (NS) was observed in the 2-4 days of observation. It is concluded that intravenous heparin therapy for a period of 2-4 days has only a minimal influence on the diagnostic lung scan classification and induces only minor changes in pulmonary vascular obstruction in the majority of patients.

Value of chest X-ray combined with perfusion scan versus ventilation/perfusion scan in acute pulmonary embolism.

BACKGROUND: The main purpose of ventilation scanning, as adjunct to perfusion lung scintigraphy, in acute pulmonary embolism is to allow for the classification of segmental perfusion defects as mismatched, which is generally accepted as proof for the presence of pulmonary embolism. We examined whether this function of the ventilation scan could be replaced by the chest X-ray. METHODS: In 389 consecutive patients with suspected pulmonary embolism and at least one segmental perfusion defect we classified the ventilation/perfusion (V/Q) scan and chest X-ray/perfusion (X/Q) scan as either mismatched or matched. Furthermore we analyzed whether this comparison was different in subgroups of patients with concomitant congestive heart failure or chronic obstructive pulmonary disease. RESULTS: Overall agreement between the X/Q and V/Q scan diagnostic category was found in 341 of 389 patients (88%; 95% CI 84-92%). The positive predictive value for obtaining a mismatched V/Q scan result in case of a mismatched X/Q scan result was 86% (95% CI 81-90%). If the X/Q scan yielded only matched defects the V/Q scan resulted in the same classification in 90% (95% CI 85-95%). Analysis of the small subgroup of patients with chronic obstructive pulmonary disease showed that a mismatched X/Q scan was confirmed by V/Q scanning in 21 of 34 cases (62%; 95% CI 45-78%). CONCLUSION: This study shows that in the great majority of patients with clinically suspected acute pulmonary embolism combination of chest X-ray with perfusion scintigraphy reliably replaced ventilation/perfusion scintigraphy in defining (mis)-matching of segmental perfusion defects. These results need confirmation before the chest X-ray can fully obviate the use of ventilation scintigraphy.